I need a constant voltage output circuit for a solar cell (Zener/Voltage Regulator?)

[ashour]

Hi,

i'm using a 6V solar cell to charge my phone using a USB cable, and it simply works out of the box to connect the vcc and gnd wires of the usb cables to the cell

The problem:

i find the output varies around 5 - 6v and i don't think this is good for the phone

My Question?

i want to get Constant Voltage Output at 5v , i've read online that i could use a ZENER diode or a Voltage Regulator for this but i don't have any clue about, any help?

Thanks

 

[Nigel Goodwin]

You shouldn't need to do anything, the output from the panel will be fairly puny anyway, and too small to be of any concern.

 

[ashour]

Great News Thanks , but it would be great if you provide me of any clue to the constant voltage output method caz i've been looking for it for several hours and i can't find any simple thing about it , and i just wannna learn about it now maybe for any other project.

Thanks

 

[Nigel Goodwin]

Great News Thanks , but it would be great if you provide me of any clue to the constant voltage output method caz i've been looking for it for several hours and i can't find any simple thing about it , and i just wannna learn about it now maybe for any other project.

Stick it straight on to a battery (via an isolation diode, which is normally built-in the panel), and it will give you constant voltage, and not waste anything - the battery limits the voltage perfectly well. You 'could' use a zener to limit the voltage, but that simply wastes the energy heating the zener, and doesn't charge the battery with it.

 

[ashour]

Thanks its working, but its a very cloud day hope that tomorrow it'll be more sunny.

 

[RCinFLA]

Many phones will refuse to initiate their charge regulator if the input voltage exceeds a certain voltage. This can be as low as 5.5 vdc for some phones.

The reason is to avoid excessive power dissipation in the phone's charge regulator series pass transistor and protect their power management chip from excessive voltage.

Solar cells are illumination based current source clamped by their inherent diode. A six volt panel with likely have 14 or 18 cells in series. Unloaded any generated current is shunted down the cell's inherent diode. This Voc voltage will be about 0.65 vdc per cell depending on temperature compared to less then 0.52 vdc per cell where most of the current is delivered to external load.

If the PV panel is unable to produce a minimum amount of current, the phone's charger input voltage will collapse possibly causing the the phone's charger to shut down. The PV voltage will then rise back up and the phone will go through the process starting up and shutting down charger over and over. Your panel should be able to deliver at least 30% of mA-H of battery in mA's at full sunlight. Typical phone normal charger current is between 60% to 80% of battery mA-H in mA's.

 

[maxx]

Maybe this solar charger will satisfy your requirements , but will take long time for a full charge .

 

[MikeMl]

Maybe this solar charger will satisfy your requirements , but will take long time for a full charge .

Unless you take the battery out of the phone, and connect to it directly, the circuit posted by Maxx, and any similar circuit, does not address the issues raised by RCinFLA. Using a solar panel that puts out less current than the Phone's AC charger is hopeless unless you use the panel to charge an intermediate battery, which then supplies a regulated 5V at a sufficient current to cause the Phone's charge controller to start up.

Obviously, the charging would go in bursts, where the intermediate battery runs down and the system waits while the solar panel recharges the intermediate battery. The final duty cycle would be dependent on the ratio of solar current to what the AC charger would supply.

 

[ashour]

Thanks All for your help,

i've actually made it and the phone is charging -without any regulation just connecting the panel the charger as i mentioned b4- but it takes too long to charge like 6 hours according to my calculations caz it took more than 2 hours to get one bar of the battery mark, and about regulating voltage i've found this circuit which is totally working - but am not using it with the solar cell just for knowledge i tried it out - Zener Diode Voltage Regulator - Electric Circuit , i just don't understand how the current intensity would flow in the output, would somebody help me with this caz i wanna understand it?

thanks

 

[carbonzit]

It would really help here to know what the current output (in mA, probably) of your solar panel is. I don't think you mentioned that (apologies if I missed it). That's what's ultimately gonna determine how long it takes to charge your battery. Do you have this information?